In recent years, as a rewritable nonvolatile memory, a magnetic random access memory (hereinafter referred to as “MRAM” as an abbreviation) has attracted attention. The MRAM stores information by using a combination of magnetization directions in two magnetic layers and detects changes in resistance (i.e., changes in current or voltage) occurring when the magnetization directions in the magnetic layers are parallel and when the magnetization directions in the magnetic layers are antiparallel to each other to read storage information.
As the MRAM, a spin torque transfer magnetization switching (Spin Torque Transfer Magnetization Switching) type MRAM has attracted attention. In the spin torque transfer magnetization switching type MRAM, for example, a magnetic tunnel junction element (hereinafter referred to as “MTJ element” as an abbreviation) is used as a magnetoresistive effect element.
The MTJ element is a magnetoresistive effect element having a configuration in which a tunnel barrier layer is interposed between a magnetization free layer and magnetization fixed layer.
In the MTJ element, when a current is caused to flow from the magnetization free layer side to the magnetization fixed layer side, electrons with a spin having the same direction as that of a spin of the magnetization fixed layer are injected into the magnetization free layer. For this reason, the direction of the spin of the magnetization free layer is equal to the direction of the spin of the magnetization fixed layer, a magnetization moment of the magnetization free layer becomes parallel, and a resistance of a magnetic tunnel junction becomes relatively small. A state in which the resistance of the magnetic tunnel junction is relatively small is associated with, for example, data “0”.
On the other hand, when the current is caused to flow from the magnetization fixed layer side to the magnetization free layer side, electrons with a spin having a direction opposing the direction of the spin of the magnetization fixed layer are reflected by the magnetization fixed layer and injected into the magnetization free layer. For this reason, the direction of the spin of the magnetization free layer is opposite to the direction of the spin of the magnetization fixed layer, the magnetization moment of the magnetization free layer is antiparallel, and the resistance of the magnetic tunnel junction becomes relatively large. A state in which the resistance of the magnetization tunnel function is relatively large is associated with, for example, data “1”.
In the MRAM using an MTJ element, when directions of a current caused to flow into the MTJ element are changed, information is written in the MTJ element. For this reason, in the MRAM using the MTJ element, two lines for writing are necessary. One of the two lines for writing is a bit line, and the other is a source line. The bit line and the source line are formed to extend in the same direction.
However, when both the bit line and the source line are simply laid out to extend in the same direction, a size of a memory cell in the extending direction of the word line becomes relatively large.